Campaigners say too little is known about electronic cigarettes
Ministers are being urged to restrict the sale of 'electronic' cigarettes amid fears they could be harmful.
Retailers say they are a healthy alternative to real cigarettes because their users can inhale nicotine without tar, tobacco or carbon monoxide.
But trading standards officers say children could buy them and be exposed to dangerous levels of the drug.
Regulation advisers want the government to restrict their sale to over 18s and require them to carry warning labels.
The 'e-cigarettes' look real, but are battery-powered and typically made of stainless steel.
Inside is a cartridge of liquid nicotine. When it is heated, the user inhales vaporised droplets of the drug and breathes out a mist rather than smoke.
First developed in China, the cigarettes were mainly bought online but are now appearing more often in street markets and retailers as consumers try to get around the smoking ban.
Last October, some retailers were reporting sales of over 1,000 of the £40 starter-packs a month.
But tests by trading standards officers found the concentration of nicotine in some products would normally need the label "highly toxic" and they are already banned in Australia.
Lacors, the body which advises local government on regulations, has called for the sales restrictions.
It is also worried that young children could swallow the small cartridges, which could prove fatal.
The World Health Organisation has raised concerns, citing a lack of knowledge about the products.
Anti-smoking group Ash has also pointed out that many of the products are made in China, where it says quality control is "not very good".
Jason Cropper, managing director of the Electronic Cigarette Company, has previously revealed that tests done on mice had shown the products to be safe, although no human trials have been done.